1. Field of the Invention.
The present invention relates to an applicator for direct or indirect application of a liquid or pasty coating medium onto a traveling material web, notably of paper or cardboard.
2. Description of the Related Art.
Applicators of the type described above are used in conjunction with so-called coaters to provide one or both sides of a traveling material web consisting, e.g., of paper, cardboard or textile material, with one or several layers of a coating medium, for example, dye, starch, impregnating fluid or the like.
In the so-called direct application, the liquid or pasty coating medium is applied by an applicating apparatus directly onto the surface of the traveling material web, which during application is carried on a revolving backing surface, for example, an endless belt or a backing roll. In the indirect application of the medium, in contrast, the liquid or pasty applicating medium, is first applied onto a substrate surface, e.g., the surface of a backing roll fashioned as an applicator roll, and is transferred there, in a nip through which the material is passed, from the applicator roll to the material web.
Known from U.S. Pat. No. 5,435,847 is an applicator with an applicating apparatus featuring a slot of constant width formed between two opposing walls, through which slot the coating medium being applied is passed onto the material web under pressure. The material web is usually carried by a backing roll associated with the applicating apparatus. This applicator additionally includes a coating edge delimiting apparatus with two coating edge delimiting elements in the form of deckle slides disposed in the slot between the opposing walls and sealing the slot on its side edges. The deckle slides are adapted to the constant width of the slot and have an essentially rectangular cross-sectional shape. Moreover, each of the deckle slides for adjustment of the coating width on the traveling material web is displaceable and fixable in the slot in a direction transverse to the direction of travel of the material web and remains during the operation of the applicator in the position once set. This prior applicator involves disadvantages to the effect that the liquid or pasty coating medium discharging from the slot often issues sideways or splashes out, depending on certain applicating or coating conditions, producing on the coated material web an untidy edge, or edge pattern, thus impairing the quality of the finished product.
Known from U.S. Pat. No. 5,436,030, furthermore, is an applicator for direct or indirect application of a liquid or pasty coating medium onto a traveling material web, notably of paper or cardboard, which applicator includes a dosing apparatus with a dosing slot fashioned as an open-jet nozzle and formed between lips on each of the approach side and the departure side. One embodiment features a deflection surface for the liquid or pasty coating medium, on the free end of the approach side or departure side. The deflection surface borders on the dosing slot and has a concave curvature. Of the two lips forming the dosing slot, the first lip, disposed on the side of the dosing slot that is approached by the applicator roll in the case of indirect application of the medium, or by the material web in the case of direct application, is termed the approach-side lip. Accordingly, the second lip, disposed on the side of the dosing slot from which the applicator roll or the material web departs from the applicator, is called the departure-side lip. In using a concavely curved deflection surface for the liquid or pasty coating medium, which borders on the dosing slot, it has been found that, depending on certain coating conditions or on the liquid or pasty coating medium used, so-called "color sails" can form on the concave deflection surface. A color sail is a thin film developing from coating medium noses that form on the side edge of the dosing slot exit, and can possibly lead to an untidy coating edge.
An applicator comparable with that according to U.S. Pat. No. 5,436,030 is being marketed by the assignee of the present invention under the trade name "Jet Flow F."